Alignment marks are used to permit precise alignment of photolithographic masks with the wafer during masking steps to minimize misalignment between multiple layers. However, the alignment marks are ‘blinded’ after non-ODR shallow trench isolation (STI) chemical mechanical polishing (CMP) processes. This prevents transfer of the lower alignment mark to the next, upper layer, for example a metal layer.
An additional photolithography and etching step (ODR) are required to clear out the silicon oxide residue from the ‘blinded’ alignment mark field. This increases costs, increases the cycle time and manufacture loading. Further, the ODR approach is limited by the circuit design rule especially as the design rule passes 0.1 μm logic and beyond.
Blind alignment marks will become a critical issue in non-OD reverse tone photo/etch (ODR) processes after 0.1 μm and beyond shallow trench isolation (STI) CMP.
U.S. Pat. No. 6,194,287 B1 to Jang et al. describes an STI process and reverse mask to clear off alignment marks.
U.S. Pat. No. 6,080,635 to Jang et al. describes discloses a method to preserve alignment marks with STI processes.
U.S. Pat. No. 6,043,133 to Jang et al. describes a process to improve STI removal over alignment marks.
U.S. Pat. No. 6,015,744 to Tseng describes a clear out and alignment mark process.
U.S. Pat. No. 5,188,258 to Iwashita describes a quantitative fluid discharge device.